Locked Admin account No access to Internet

HI, our school Mac books were locked to the school server which a new support team closed down (only backing up data). New server is PC and we had wanted to keep old server and old macs but are unable to access as they appear to be 'searching' for server which is no longer there.

Can anyone help giving instructions to access MacBooks (won't access internet at home as admin permission locked).

Would it it be sorted if I can change admin rights and if so how do I do that?

P.s. Our tech support are not Mac savvy!